With that many Indians I’m not so sure a Gatling gun would’ve made much a difference.
Custer was offered a couple of Gatling guns but turned them down because they would have slowed him down. I don't think they could have been brought to bear at Last Stand Hill but they very well may have saved him by slowing him down enough that he and General Terry's troops coming in from the north would have converged on the camp simultaneously on the 27th. The Indians had problems defeating infantry or as they called them "walking soldiers".
